THE 220-year-old home of a freed Montclair slave named James Howe is in danger of being uprooted, dragged through town and perched next to the house of his old master. The current owner of the small, two-story Howe House has agreed to donate it to the Montclair Historical Society so it can be preserved as a showcase for the black experience in that town. But the Howe House may be physically damaged by a move, and there is no guarantee that the historical society will manage the house properly when it reaches its new site.